1. Field of the Invention
The invention relates to downhole systems for controlling the flow of fluids from petroleum production wells and, more particularly, to a power supply and control arrangement for a submersible pump and solenoid operated safety valve system.
2. History of the Prior Art
Oil and gas wells, and in particular those located offshore, are frequently subject to wellhead damage which may be produced by violent storms, collisions with ships and numerous other disasterous occurrences. Damage to the wellhead may result in the leakage of hydrocarbons into the atmosphere producing the possibility of both the spillage of the petroleum products into the environment as well as an explosion and fire resulting therefrom. In addition to off-shore production wells, another environment in which damage to a wellhead may have disasterous effects is that of producing wells located in urban areas. Moreover, in such urban production wells it is generally a specific legal requirement that there be some downhole means of terminating the flow of petroleum products from the well in the event of damage to the wellhead. In such instances, the safety valve must be responsive to a dramatic increase in flow rate from the well so as to close down and terminate production flow from the well. For these reasons, sub-surface safety valves located downhole within the borehole have long been included as an integral part of the operating equipment of a petroleum production well.
Various types of petroleum production flow safety valve systems have been provided in the prior art. Each system includes a valve means for controlling the flow of petroleum up the tubing from a point down in the borehole from the wellhead. Safety valve systems include sensing means which are responsive to wellhead damage, a dramatic increase in production flow or some other emergency condition requiring that the flow from the well be terminated by the valve.
One type of operating mechanism to actuate a safety valve within the well is shown in U.S. Pat. No. 3,861,464 to Boyadjieff et al which includes a mechanical actuation means comprising an elongate cable extending from the wellhead down to the safety valve whereby movement of the cable effects opening and closing of the valve. Such mechanical actuation systems are severely limited with respect to the depth to which such systems are operable and also include the inherent disadvantages of potential stickage, cable stretching and other mechanical failures affecting operation of the valve.
The most common method for controlling downhole petroleum flow safety valves is that of a hydraulic control line extending from a pressure reservoir at the wellhead down the borehole to the safety valve. Generally, safety valves are spring biased into a closed condition and opening the valve to allow production flow requires the application of a hydraulic pressure to overcome the spring bias and hold the valve in an open condition. In the event of a failure of the hydraulic system or damage to the wellhead or to the hydraulic line, release of the hydraulic pressure allows the spring to automatically close the safety valve thereby providing a safe operation. One such system is shown in U.S. Pat. No. 4,160,484 to Watkins. A related type of hydraulic control system for safety valves is one in which the flow of the production fluid produces a pressure which is balanced against a control hydraulic pressure from the wellhead. In the event that the flow produced pressure becomes much greater, for example due to runaway production flow through the valve, this flow produced pressure overcomes the control pressure and closes the safety valve in response to the emergency flow condition. Such a system is shown in U.S. Pat. No. 3,750,700 to Ecuer.
All hydraulic pressure controlled safety valve systems have certain inherent disadvantages. One limitation is the depth to which the system is operable. That is, the length of the line through which the hydraulic fluid is operable determine the final downhole operating pressure of the fluid. In very deep wells this produces an extremely high operating pressure at the safety valve. In some cases the downhole hydraulic pressure becomes so great at a certain depth that it cannot be overcome by spring biased type systems. This in effect renders such a system, which would otherwise be perfectly effective in shallower wells, less useful in very deep production situations. In addition, the hydraulic pressure in closed static hydraulic pressure circuits often become extremely high which produces a very dangerous condition both within the well and for personnel working around and with the hydraulic system at the surface.
Some of the disadvantages of hydraulic and mechanically actuated safety valve systems are overcome by the use of an electrical solenoid to operate the safety valve in a downhole production environment. Numerous such systems have been proposed, for example, U.S. Pat. No. 4,002,202 to Huebsch et al, U.S. Pat. No. 4,161,215 to Bourne, Jr. et al, and U.S. Pat. No. 4,566,534 Going III. Such systems provide a solenoid actuated operating mechanism for the safety valve which is responsive to a DC electric current supplied from surface equipment. Such solenoids generally require a fairly high level surge of initial operating current to cause the solenoid to change states and then a smaller level of current to hold the solenoid in its new operating condition. These large actuating current surges require heavy electrical conductors in order to carry such current downhole for any substantial distance and still maintain a voltage level sufficient to operate the solenoid.
In hydrocarbon producing formations where there is sufficient reservoir pressure to cause formation fluids to flow spontaneously to the well surface, only flow control valves are required to regulate the flow of fluids up the tubing. However, in well production environments in which the natural reservoir pressure is lower than that required to produce a desired flow rate of fluids from the well, it is frequently necessary to use an electrically powered submersible pump down in the well in order to achieve the desired hydrocarbon flow rate. Such submersible pump actuated systems also necessitate the use of a subsurface safety valve for the reasons discussed above. In most production systems which include electrically operable submersible pumps it is conventional to employ a hydraulically controlled safety valve such as is shown in U.S. Pat. No. 4,529,035 to Bayh and U.S. Pat. No. 4,354,554 to Calhoun et al. Moreover, in U.S. Pat. No. 4,425,965 to Bayh et al the hydraulic output of the pump itself is used to provide actuating pressure for the hydraulically actuated safety valve.
Electrically operated submersible pumps require an electrical transmission line for AC power, generally in a three phase configuration, from the wellhead downhole to the pump in order to drive the electric motor powering the pump. Conventional submersible pump production systems have also required a hydraulic transmission line extending from the wellhead to a location near the submersible pump in order to provide an actuation and control circuit for the hydraulically actuated safety valve used with the pump. Such conventional production equipment configurations thus require redundant circuits, one electrical and one hydraulic. Such circuits also necessitate two mutually independent actuation and control systems which are not interfaceable directly with one another.
There are certain disadvantages inherent in the combination of an electrically operated submersible pump and an electrically operated safety valve. One disadvantage is that while AC power is required to actuate the pump, DC power is usually necessary to operate the solenoid actuating the safety valve thus requiring a large expenditure on redundant electrical cable, one for AC and one for DC.
The system of the present invention overcomes many of the inherent disadvantages of the prior art solenoid operated safety valves systems as well as enables the practical combination of a submersible pump and an electrical solenoid actuated safety valve into a single system.